The present invention relates generally to reflective articles having information-bearing indicia thereon. The invention has particular application to such articles which are polymeric.
The term "retroreflective" as used herein refers to the attribute of reflecting an obliquely incident light ray in a direction antiparallel to its incident direction, or nearly so, such that it returns to the light source or the immediate vicinity thereof. The term "patterned" when used in connection with the term "retroreflective" refers to an information-conveying design or image, and is to be distinguished from patterns such as simple seal cell polygonal shapes which do not convey significant information. Other terms are defined in the glossary at the end of the specification.
PCT Publication No. WO 95/17692 (Ouderkirk et al.), incorporated herein by reference, discloses multilayer polymeric films configured as reflective polarizers in combination with various structured surface materials which confine light to a relatively narrow viewing zone. Multilayer films having birefringent layers are discussed, including films where the out-of-plane refractive indices of adjacent layers are matched. Structured surface materials include those having a plurality of triangular prisms as well as symmetric cube corner sheeting. A discussion of the multilayer films configured as mirrors is also included.
It is known from U.S. Pat. No. 5,353,154 (Lutz et al.) to print indicia on at least one surface of a reflective polymeric body to illuminate information upon exposure to a back light source and to conceal such information when not exposed to light. The reflective polymeric body is provided with a first and second diverse polymeric material arranged in substantially parallel alternating layers, and a sufficient number of layers is provided such that the body reflects at least 40% of light impinging on a first major surface thereof while transmitting at least 5% of light directed through a second major surface thereof.
It is known from U.S. Pat. No. 4,175,775 (Kruegle) to provide a photo I.D. card with a photographic image hidden behind a filter region and placed in front of a high gain retroreflective material. The filter region absorbs virtually all of the light impinging on it, and may comprise a half-silvered mirror but "advantageously comprises" a filter material which transmits infrared or ultraviolet light but blocks substantially all visible light.
Retroreflective sheeting with printed indicia thereon, such as the ubiquitous traffic control "STOP" sign, is also known, as is retroreflective sheeting with directional images formed therein (see, e.g., U.S. Pat. No. 4,708,920 (Orensteen et al.)).
Two known types of retroreflective sheeting are microsphere-based sheeting and cube corner sheeting. Microsphere-based sheeting, sometimes called "beaded" sheeting, employs a multitude of microspheres typically at least partially imbedded in a binder layer and having associated specular or diffuse reflecting materials (e.g., pigment particles, metal flakes, vapor coats) to retroreflect incident light. Illustrative examples are disclosed in U.S. Pat. Nos. 3,190,178 (McKenzie), 4,025,159 (McGrath), and 5,066,098 (Kult). Cube corner retroreflective sheeting comprises a body portion typically having a substantially planar front surface and a structured rear surface comprising a plurality of cube corner elements. Each cube corner element comprises three approximately mutually perpendicular optical faces. Examples include U.S. Pat. Nos. 1,591,572 (Stimson), 4,588,258 (Hoopman), 4,775,219 (Appledorn et al.), 5,138,488 (Szczech), and 5,557,836 (Smith et al.). It is known to apply a seal layer to the structured surface in a regular pattern of closed polygons which form isolated, sealed cells to keep contaminants away from individual cube corners. Heat and pressure used to form the cells destroys or deforms cube corner elements located along the polygon boundaries. Flexible cube corner sheetings such as those disclosed in U.S. Pat. No. 5,450,235 (Smith et al.) are also known and can be incorporated in embodiments described below.
There is a continuing need for novel polymeric-based articles which can selectively display information. Such articles can be incorporated in a variety of end use applications such as document authentication, toys, games, and decorative articles.